In the dark, cold clouds of space where stars are born, dust grains become coated with a thin layer of ice. This ice is not just frozen water but a mixture of different molecules: carbon monoxide, carbon dioxide, nitrogen, and others. For a long time, astronomers could not find nitrous oxide (N2O) in this ice — the very "laughing gas" used in medicine. They had been searching for it since the launch of the ISO infrared observatory in 1995, but without success.
Now, the James Webb Space Telescope with its sensitive instruments has allowed a deeper look. Scientists took spectra of 50 protostars — objects that are just beginning to shine. In these spectra, they looked for the characteristic absorption band of nitrous oxide at a wavelength of about 4.45 micrometers. To accurately identify it, they prepared in the lab ices with different proportions of N2O, CO2, CO, and N2 and measured how they absorb infrared light.
The result: for the first time, nitrous oxide has been reliably detected in solid form around 16 protostars. Moreover, it sits not deep within the icy crust but in its outer, non-polar layer, where there is plenty of carbon monoxide and nitrogen. The fraction of N2O there is small — from 0.2% to 2.1% compared to carbon monoxide. It's like finding a pinch of salt in a bowl of sugar: a little, but significant.
The discovery helps us understand what substances were in our "building material" before planets formed. Possibly, some of the nitrogen and oxygen that make up life passed through a stage of such icy grains. Now astronomers have a reliable way to search for nitrous oxide in other cold clouds and to track how it changes as new stars are born.
Nitrous oxide in space is the same gas that dentists use for mild anesthesia, only frozen into ice at a temperature of about -260°C.
In Arthur C. Clarke's novel "2010: Odyssey Two," an ocean lies beneath the ice on Europa, where unusual chemical reactions might occur — similar to how molecules important for future life are born in the icy mantles of protostars.